Poor level of information around ID sync process

Issue in ./help/destinations/catalog/advertising/google-dv360.md

The docs mention an ID sync is required, but the process to enable the ID sync is not documented other than via DIL code customisations. The docs should include examples of the ID syncs happening on page to give customers examples of how it will look once enabled - this has been asked for multiple times.

Additionally for customers who do not have AAM, it needs to be clear what needs to be done to enable the AAM UUID to be captured (even if it is done in the background automatically).

Start with ./help/destinations/catalog/advertising/google-dv360.md and review its existing ID sync and DIL customization references. Done means documenting how to enable ID sync, showing examples of the resulting page activity, and clarifying how the AAM UUID is captured for customers without AAM.

Written by the indexing model from the issue text.